An apparatus of this kind, described in the Swedish Patent Application No. 0202622.7, may be used for instance for cleaning of crankcase gas coming from an internal combustion engine. The centrifugal rotor may be driven for instance by means of pressurized lubricant coming from the same combustion engine, and the driving device may comprise a turbine member, which is supported by the drive shaft in the drive chamber, and a spray device, which is arranged to spray a liquid against the turbine member in the drive chamber for rotation of the drive shaft and thereby the centrifugal rotor.
For avoiding that pressurized liquid upon operation of an apparatus of this kind would unintentionally pass upwardly along the drive shaft from the drive chamber to the separation chamber and thereby deteriorate gas having been cleaned in the separation chamber but having not yet left it, a sealing device has to be arranged between the drive shaft and said bottom, through which the drive shaft extends. It has proved difficult, however, to get a sealing device to prevent completely transfer of liquid from the drive chamber to the separation chamber, particularly if a bearing is to be arranged between the drive shaft and said bottom.